In certain aspects, the present invention represents improvements over the bulk materials handling machines disclosed and claimed in the present applicant's U.S. Pat. Nos. 3,378,130, issued Apr. 16, 1968, and No. 3,688,893, issued Sept. 5, 1972. The present invention also represents improvements over the machine disclosed in U.S. Pat. No. 4,264,003, issued Apr. 28, 1981 to Charles B. Gill. The bulk materials handled by such machines may include granular materials, powders, flakes, chips or the like.
These bulk materials handling machines utilize an endless bucket train comprising many axially spaced circular buckets connected together by flexible tension elements, such as cable means. The bucket train is supported and driven by a series of wheels to define separated loading and unloading spans of buckets.
The loading span is defined by two such wheels, horizontally spaced apart and disposed above the loose bulk material that is to be dug and conveyed by the materials handling machine. Initially, in the free state, the bucket train in the loading span is freely suspended along a catenary curve between the two wheels. However, when the machine is in use, the loading span is brought into digging engagement with a pile or mass of the loose bulk material. In this situation, an intermediate section of the loading span engages the bulk material and is deflected upwardly from the catenary curve. As the bucket train is circulated, the initial or downward section of the loading span is moved with empty buckets from the first of the wheels to the bulk material, the intermediate section of the loading span is dragged through the material to fill the buckets, and the other end section of the loading span is moved with filled buckets upwardly from the material and toward the unloading span.
The unloading span of the bucket train may be elevated above the loose material and located downstream therefrom, relative to the direction of movement of the bucket train, and operates to dump the material from the buckets, as, for example, into a hopper or onto a take-away conveyor. In one advantageous arrangement of the unloading span, the bucket train travels over a first wheel and under the next wheel, which is located lower than the first wheel, whereby the buckets are inverted between these wheels, so as to dump the material from the buckets.
Each bucket may have a circular cross section and may include a central tubular mounting core. The tension elements may be made of flexible wire rope or cable and may extend into the mounting cores at both ends of the buckets, which may be secured to the tension element means at generally equal axial spacings therealong. The bucket train is adapted to ride around on the periphery of each conveyor wheel.
Each wheel may have spaced guides to receive and laterally hold the cable means between each pair of adjacent buckets. Each bucket fits between each pair of adjacent guides. Drive rollers or other means are mounted on the periphery of each wheel, for meshing with the bucket train, between the spaced buckets, so as to keep the movements of the bucket train and wheel synchronized. One or more of the wheels typically are rotated under power, to circulate the bucket train, while the remaining wheels are idler wheels, rotated by the moving bucket train. As to the power driven wheels, the drive rollers engage a rounded bottom portion of each bucket, to drive the bucket train. As to the idler rollers, the drive rollers are engaged by the core at the top end of each bucket, so that the wheel is driven by the bucket train. Additional rollers or other supports may also be provided on the periphery of each wheel, to engage and stabilize the buckets as they are carried around on the wheel.
To recapitulate, the buckets are held in place on each wheel by the support rollers, engaging the sides of the buckets, by the drive rollers, engaging the bottoms or tops of the buckets, and by the cable guides, on which the cables or tension elements are trained.
In the typical bulk materials handling machine as described, the cable or wire rope sections, extending between the buckets, must support the total weight of the suspended filled buckets of the loading span. An additional significant load can be imposed on the cable sections because of the buckets digging through the bulk material. Centrifugal forces tending to whip the buckets out from the wheels are also generated, and must be resisted by the cable sections. Moreover, the cable sections are repeatedly flexed as they move over each support wheel and assumes its curvature. These stresses of course set the minimum design specifications for the cable or wire rope sections.
For a high payload capacity machine, the buckets are made large, thus imposing very large loads on the cables. Moreover, the bucket train may also be operated at a high speed, so that the cables are subjected to severe flexure and vibration under heavy loads. Field experience with such bulk materials handling machines indicates that cable maintenance and failure constitute the most common cause for machine downtime. The repeated flexure of the cables, proximate the buckets, the abrasion of the cables against the cable guides, as the cables travel around on the support wheels, and the high cable loads and stresses are all believed to be contributing causes for cable failures. Even with optimim cable design, combining high strength and high flexibility, there has been and unexpectedly high incidence of cable damage, such as fraying, and actual cable failure.